<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
         /* 伪类选择器 */
         .box
         {
             width: 100px;
             height: 100px;
             background-color: salmon;
         }
         .box:hover
         {
            background-color: blue;
         }
    </style>
</head>
<body>
    <div class="box"></div>
</body>
</html>